Solvent extraction of normally liquid hydrocarbons



, w 1942- R. K. STRATFORD ETAL 2,302,333

SOLVENT EXTRACTION OF'NORMALLY LIQUID HYDROCARBONS Filed Dec. 7, 1938 WA T522 MQET P4 RArFnv/ C. FZA c 7"/0N.S sTona 65 .222 um 7'25 A T/N 6 XTRACT LINE GLYCOL A/A'P/l THA 501 px. v SUPPLY 7H NK 2 A 714 /w 5771.1.

TiE/ETHYLENE GLYCQL LINE A oMAT/c TRACT/0N5 STORAGE TANK Patented Nov. 17, 1942 SOLVENT EXTRACTION OF NORMALLY LIQUID HYDROCARBONS Reginald K. Stratford, Corunna, and George W. Gurd, Sarnia, Ontario, Canada, assignors to Standard Oil Development Company, a corporation of Delaware Application December 7, 1938, Serial No. 244,322

high yields of extracts highly aromatic in nature. For example, most naphthas contain both parafiinic and aromatic hydrocarbons. The relative quantity of each of these constituents varies 7 Claims.

The present invention relates to the solvent extraction of normally liquid hydrocarbons. The invention is particularly directed to the solvent treatment of lower boiling hydrocarbons of the type of naphtha, heavy naphtha, kerosene, and with the source from which the naphtha is oblight gas oil. The invention especially relates to tained. Thus, for example, naphthas derived an improved method of separating the aromatic. from asphaltic crudes such as California, are constituents from the paraflinic constituents of generally rich in aromatic,hydrocarbons; wheresaid normally liquid hydrocarbons. In accordas naphthas obtained from paraffin base crudes ance with the process of the present invention, such as Pennsylvania, are rich in parafiinic hyhydrocarbons are treated with a solvent selected drocarbons. It has been found that naphthas from the class of dihydric alcohols characterized rich in aromatic hydrocarbons are better motor by having at least one ether group. The present fuels from the standpoint of knocking characapplication is a continuation-in-part of our ap teristics than naphthas rich in paraffinic hydrop1icati0nSer.No. 39,880, filed September 10, 1935, 1 ar ons. A C nv i d x f t n k entitled, Solvent extraction of lower boiling characteristics of a naphtha is the octane hydrocarbons, number. The octane number is high for naph- It is well known in the art to treat petroleum thas of low knocking tendency and low for oils with various solvents in order to separate the naphthas of high knocking tendency. The relatively more paraflinic constituents from the knocking characteristics of naphthas to be used more aromatic constituents. In these processes, as motor fuels are of prima y importance, o t at solvents of the class which 'have a preferential it can be seen that it is desirable to obtain selectivity for the more aromatic type constituap t -S Which are rich in aromatic y oents are usually employed. Solvents of this class carbons. are, for example, phenol, nitro benzene, sulfur t is, t r an Object of the P s nt ndioxide and the like. It is also known to use v n n t p v a means fo ra n n p other substances, as for example, liquefied thas and other relatively low boiling hydrocarbon normally gaseous hydrocarbons in conjunction fractions into their respective paraffinic and with the above class'of solvents. It is the usual aromatic constituents. The aromatic fractions practice to contact the oil and solvent in a thereby obtained may then be used either as countercurrent treating tower operation. In this mot r fue s emse v s 0 a di ents operation the heavier phase, usually the solvent, for other naphthas Of relat y ower Octane is introduced at the top of a countercurrent number. treating tower and the lighter phase, usually cco d ng to the present invention, low boilthe oil, is introduced at the bottom of said tower. ing hydr car on fr t ns ar s p ra d into The respective phases flow countercurrently their more parafilnic and their more arounder conditions to cause phase separation. A matic fractions by means of a selective solvent. solvent rich or extract phase highly aromatic in For purposes of this nature, the ideal selective nature is withdrawn from the bottom of said solvent is one which has the following charactertower, while a solvent poor phase or raffinate istics: (1) high selectivity as between paramnic phase highly parafilnic in nature is withdrawn and aromatic hydrocarbons, that is to say, a from the top of the tower. The solvent extract solvent which has substantially no solubility for phase and raffinate phase are then subjected to parafiinic fractions and very high solubility for treatment in order to separate the solvent from aromatic fractions; (2) stability; (3) high boilthe respective phases. The operation is usually ing point; (4) high Selectivity at pe atures conducted at atmospheric pressure. although epploXimeting normal p atures to avoid the other pressures may be employed. The temperacessity of heating or refrigeration; (5) easy ture employed is in the range between the meltseparation of phases; (6) easy separation of the ing' point of the solvent and the temperature at solvent from the extract phase, either by distil which complete miscibility occurs between the lation or other means; and (7) relatively high solvent and the oil. Similar results are also sesolubility for aromatic fractions in order to avoid cured bya batch or semi-batch operation. the use of large quantities'of solvent.

The processes heretofore employed. however, 7 We have now discovered a class of solvents have not been entirely satisfactory, especially in which are particularly adapted for the separathe treatment of lower boiling hydrocarbons, 5 tion of low boiling hydrocarbons into their relasince it was not possible to economically secure tively mor aromatic n Darafiinic fractions.

. derstood that the treatment may be col 3 will depend upon the particular petreleu The solvents of our invention meet the above enumerated desirable characteristics, giving high yields of high quality products, The solvents of the present invention are selected from the class of oihydric alcohols which are characterized by having at least one other group. Dihydric gly-,

cols having atleast one ether group, as for example, diethylene glycol, triethylene glycol, and tetraethylene glycol, are especially desirabe.

The process of our invention may be readily understood by reference to the attached drawing illustrating one modification oi the invention. For the purposes of description the solvent being treated is assumed to be triethyiene glycol and the oil being treated is naphtha.

Referring to the drawing, numeral designates a supply tank of triethyiene glycol, nu.- nieral 2 designates a supply tank or" naphtha to be treated and numeral 3 designates a treating tower which may consist of a plurality of stages and is adapted to be operated in a countercurrent manner. Naphtha is withdravm from tanl; 2 through line 5' by means of pump and intro duced near the base oi tower through line Triethylene glycol is withdrawn from tank i through line i by means of pump 8 and introduced into the upper portion of tower 3 through line 9. In tower 3 the naphtha and triethylene glycol flow in countercurrent relationship.

The raiinate consisting of the parafiinic fractions of the oil is withdrawn from the top of the tower through line iii. it will be found to con tain only a trace of triethylene glycol which may be removed by washing the rafiirrate with Water. For this purpose, the raitinate is introduced into separation drum ii, Water is introduced through line it, whereupon two phases are formed, the lower phase consisting oi water and triethylene glycol and the upper phase consisting of the parafinic naphtha fraction. The tr'iethylene gly col-water phase may be removed from drum it through line it and the triethylene glycol may be recovered and recirculated to the process if de sired. The parafinic naphtha fraction E re moved from drum 5 l through line it and collect ed in the storage drum 3%. it is to be understood that the triethylene glycol may be removed by washing the raflinate phase in a countercurrent tower rather than in drum ii. I

The extract consisting of the bulls oi the triethylene glycol '"and" the aromatic fractions or the naphtha i withdrawn irorn tower a through line H3 and introduced into still i'i, wherein the hydrocarbons are separated from the triethylene glycol. The hydrocarbon fractions are removed through the top of the still through line i8, condensed in cooler is and forwarded through line to storage drum 2%. 'iriethylene glycol which is not vaporized at the still temperatures is removed therefrom gthreugh line it and returned by means of pump-2t and line '28 to supp y tank i.

in the operation of the process, it Will be unled out either in a countercurrent or batch marine The temperature maintained in treatinr tower ii being-treated, as well as upon the solvent being used and the yield and quality of products desired. When treating-naphtha with triethyieoe glycol, the temperature is preferably nrairrtained between about 50 and 1 i513" F around more. It is preferred to employ atmospheric pressure, although other pressures may be employed. in the even light naphtha is treated it may be le, for example, to w asoaass treat at a higher pressure in order to avoid vaporization of the light fractions of the naphtha.

The volume of solvent used per volume of oil likewise will depend upon the particular oil being treated, as Well as the solvent employed. In general, it is preferred to use from about 3 to 5 volumes of solvent per volume of oil, although at times it may be desirable to use from 2 to 5 volumes of solvent per volume 01' oil.

The solvents of the present invention are readily recovered from the extract and raffinate phases by distillation since the solvents have rel" atively high boiling points. Vacuum distillation extract and rafiinate phases by the addition of 1 water or other solvent for dihydric alcohols which is immiscible with the petroleum oil, It is to be understood that a portion of the extract may be re-introduced into the counter-current treating tower.

In some cases, particularly when extracting refined naphthas, .it may be desirable to add benzol, phenol, chloroform and similar substances to the diethylene and higher glycols in order to increase their solubility for the petroleum oil. It is to be understood that the selectivity and solvent power of the dihydric alcohols may be modir'led to any desired extent by the addition of water or similar agent thereto at one or more stages.

The extract obtained according to the present process may be used directly as a motor fuel or as a blending agent for other naphthas. It may also be subjected to other treatments such as'hydrogenation, in order to increase its octane number.

it will be understood that the present process is not limited to low boiling hydrocarbons ob tained from any particular source, but is of general application to all types of low boiling hydrocarbons of the type or naphthas, kerosenes, and r A Com'oe naphtha or the following characteris= tics:

Refractive index at 20 C 1.4377 ALP. I. gravity 49.3 Initial boiling point ..F 218 l B. 1- F 324 50% point F 244 was treated countercurrently with 300% triethylone glycol at a temperature of F. The characteristics of the extract and rafflnate obtained are given in the following table:

Eitract Reillnate Refractive index at 20 0.. 1.4770 1. 4225 A. P. I. gravity 36.7 54.4 Yield on charge per cent.. 27. 5 72. 5

Similar experiments carried out on the same naphtha using 600% triethylene glycol instead of 300% gave the following results:

Extract Raiiinate Refractive index at 20 C p 1.4750 1' 1.4152 A. P. I. gravity f. 37. 1 57. 2

Yield on charge .per cent J 43 57 In the above examples the low gravityphigh refractive index and the aromatic odor of the ex tracts indicate that the triethylene glycol; has made a well defined separation of the naphtha into parafflnic and highly aromatic constituents.

Example 2 j Various operations were conducted to deter- {nine the solubility of aromatic hydrocarbons in various glycols. These operations were connoted at a temperature of 70 F. and the results secured were as follows:

[Percent by volume of aromatic soluble in solvent (based on solvent volume)] Mono- Dieth- Trieth- Tetraethethylene ylene ylene ylene glycol glycol glycol glycol Per cent Per cent Per cent Per cent Benzene. 1 40 95 Toluene. 20 30 90 Xylene 10 20 35 Various operations were conducted to determine the solubility of aromatic materials in ethlene glycol, diethylene glycol and triethylene glycol at various temperatures. The results of @4358 operations were as follows:

Ethylene Diethylene 'Iriethylene Per cent Example 4 The following data summarize the results secured when treating a feed stock, comprising one 7 volume ofbenzene, two volumes of toluene, and

two volumes of xylene present in an aromaticfree Mid-Continent naphtha to make a total aro-' matic concentration of 57%, with 43% by volume of tetraethylene glycol:

It will be observed that a single batch treat produced a 10% yield of extract containing 91% pure aromatics. Additional operations disclosed the fact that the solubility of aromatics in tetraethylene glycol increased rapidly with increasing 7 temperature. Thus, this solvent may readily'be employed in an operation in which the extraction stage is conducted at a relatively high temperapurposes of illustration, but is limited only in and by the following claims in which it is our intention to claim all novelty inherent in the inven- 1 tion.

prises extracting the hydrocarbon fraction with a solvent consisting essentially of a substance selected from the class of dihydric glycols characterized by having at least two ether groups.

3. Process for separating a hydrocarbon fraction of the class of naphtha, kerosene, and light gas oil into its relatively more paraffinic and relatively more aromatic constituents, which comprises extracting the hydrocarbon fraction with triethylene glycol.

, 4. Improved process for separating a hydrocarbonfraction of the class of naphtha, kerosene and-light gas oil into relatively more paraflinic and more aromatic constituents which comprises countercurrently contacting said hydrocarbon fraction in liquid phase with a solvent consisting essentially of a substance selectedfrom the class of dihydric alcohols which are characterizedby having at least two ether groups underconditions to form a raflinate phase and a solvent extract phase, separating the respective phases and removing the solvent therefrom.

.5. Process in accordance with claim 4 in which said solvent is triethylene glycol.

6; Process in accordance with claim 4 in which the solvent is removed from the respective phases by washing with water at ordinary temperature.

'7. Process forse'parating a normally liquid hydrocarbon into its relatively more parafiinic and relatively more aromatic constituents which comprises extracting the hydrocarbon fraction in liquid phase with a solvent mixture comprising a substance selected from the class consisting of benzol and phenol and containing at least 50% of a substance selected from the class of dihydric alcohols characterized by having at least two ether groups.

REGINALD K. S'I'RA'I'FORD. GEORGE W. GURD. 

